The present invention relates to an optical equipment and, more particularly, to an optical equipment such as a video camera, silver halide camera, electronic still camera, or the like, which comprises an optical system (photographing optical system) having a movable lens group that moves along the optical axis upon focusing or zooming, e.g., an optical system such as a photographing lens of a single focal length, zoom lens, or the like, its control method, and a storage medium.
Conventionally, in case of a rear-focus zoom type lens, the stop positions of a variator used in zooming and a focus lens used in focus adjustment on the optical axis change in units of object distances, as shown in FIG. 1 (these curves will be referred to as “cam loci” hereinafter). Referring to FIG. 1, for example, when the object distance is infinity (or 2 m), the focus lens (RR lens) moves on the optical axis along convex locus Y∞ (or Y2) toward the object side upon movement of the variator from the wide-angle end to the telephoto end on the optical axis.
That is, conventionally, upon zooming from the wide-angle end to the telephoto end or vice versa, when driving of the variator and focus lens is controlled to trace the cam locus in correspondence with the object distance, a good image free from any blur is obtained. That is, conventional cam trace is to merely track the stored cam locus.
However, an optical system and mechanical system normally suffer manufacturing errors, and it is difficult to match their movements with the theoretically obtained stored cam locus. It is also impractical to require of commercial products higher precision in the optical system and mechanical system to attain matching. In addition, with the conventional technique and camera precision, a given blur range cannot be visually recognized. However, as the image quality and magnification become higher in recent years or in the future, such blur range may be easily recognized.
Furthermore, it is important to attain high-precision cam trace with less labor and lower cost.
Also, in an exchangeable lens system that uses an exchangeable lens, an attachment having a zoom effect is normally interposed between lens and camera apparatuses (the attachment will be referred to as an extender hereinafter). However, upon mounting the extender, the cam locus becomes considerably different from that without the extender.
Upon zooming, since the cam loci in units of object distances become denser toward the wide-angle position, as shown in FIG. 1, a cam locus corresponding to a given object distance cannot be accurately selected upon zooming from the wide-angle end to the telephoto end, and the initially selected cam locus may slightly deviate from that corresponding to the object distance.
In such case, blurring takes place upon zooming. For example, upon zooming from the wide-angle end to the telephoto end, when a cam locus corresponding to a non-in-focus object distance (e.g., 1 m) is selected and traced for an object at an object distance (e.g., 2 m) which does not correspond to the original in-focus locus, no blur (deterioration of the in-focus level) is not formed near the wide-angle end, but blur is produced from the middle focal length to the telephoto end. Also, when the object distance changes upon, e.g., movement of an object, an in-focus state cannot be attained by the cam locus traced so far, thus producing a blur.
In order to solve this problem, the following processing is done. That is, the in-focus level is checked by sampling an auto-focus signal (to be referred to as an AF signal hereinafter) at predetermined periods from a video signal obtained from a photoelectric conversion element such as a CCD during zooming. The in-focus level obtained by the previous sampling is compared with that obtained by the current sampling to find a cam locus with higher in-focus level, and the cam locus is traced while changing the cam locus to that with higher in-focus level.
In this case, the AF signal is detected in synchronism with the vertical scanning frequency of the television format used in a video camera in case of the video camera. That is, the AF signal is sampled at a frequency of 50 Hz when the PAL format is used or at 60 Hz when the NTSC format is used. Note that one period will be expressed by 1V or V hereinafter.
As the image quality and magnification become higher, addition of a function that allows the photographer to take a broad range of pictures is required. Especially, demands for ultra-low-speed zooming, i.e., so-called “artistic zooming”, and ultra-high-speed zooming for changing the field angle from the telephoto end to the wide-angle end or vice versa as quick as possible are very large.
However, when the zooming speed is varied over a broad range from ultra high speed to ultra low speed, in case of ultra-low-speed zooming, blur is produced in practice, but the in-focus level obtained by the current sampling remains the same as the previous value in relation to the sampling period of an AF signal, and the cam loci cannot be changed. As a result, the control halts in a blur state. This problem occurs conspicuously when a stepping motor is used to drive the variator or focus lens, since such motor has a drive halt period.
Also, when the zooming speed is varied over a broad range from ultra high speed to ultra low speed, if the focus lens moving amount is corrected in consideration of the in-focus level alone without taking the zooming speed into consideration like in the conventional system, the focus lens moving amount remains the same irrespective of the zooming speed when the in-focus level remains the same, thus posing the following problem. For example, upon ultra-high-speed zooming, the focus lens moves too much and overshoots the in-focus cam locus to be selected, and blur stands out. By contrast, upon ultra-low-speed zooming, a long time is required until the in-focus cam locus is reached.